The present invention is a development from my prior U.S. Pat. Nos. 3,948,344; 4,155,421; and 4,298,083; directed to flexible film air pallets for transporting relatively heavy loads across surfaces with minimal frictional restraint. While the term "air pallet" designates a load support system for the moving of loads on an air film, such term is not limited to replacements for wooden pallets normally moved by fork lift trucks and the like. The air pallets of the patents above are in all respects vehicles, that is, they support a load on an air film, and they permit the load to be moved over an underlying generally planar support surface. Such techniques have been applied to air lifted and propelled vehicles as for instance is the subject matter of copending U.S. patent application Ser. No. 365,520 filed Apr. 5, 1982, now abandoned, of which I am a coapplicant.
The subject matter of the issued patents and copending patent application Ser. No, 365,520 involves a flexible film sheet (or its equivalent) sealably fixed about its edges directly beneath a load or to a load bearing surface and a plenum chamber developed between the sheet and a relatively rigid backing member which could be an element of the load itself. The sheet is perforated within an area lying beneath the load. Low pressure air entering the plenum chamber is distributed by dispersion means which may constitute elements of the backing member, and low pressure air discharges at low flow rates from the plenum chamber through the large number of minute perforations in the flexible sheet to create an air film which raises the pallet or vehicle off the underlying support surface. With the plenum chamber collapsed and the perforated area of the flexible sheet pressed against the underlying support surface, pressurizing the plenum chamber initially jacks the load. The air then tends to escape through the perforations of the flexible sheet and a condition is reached where a number of the perforations open directly to the atmosphere terminating jacking with the creation of a thin frictionless air film beneath the flexible sheet and between that sheet and the underlying generally planar support surface.
The load carrying footprint thereby defined must be sufficiently large to avoid tipping of the load. If the pressurization of the plenum chamber is too high, the flexible sheet balloons, the plenum becomes too large, the flexible sheet becomes too rounded, the footprint becomes too small, and the load becomes unstable and may tip. The portion of the flexible sheet at its edges is not perforated purposely to achieve jacking of the load. The perforations define the "footprint" while the non-perforated portion permits the air pallet to ride over obstructions as it travels across the generally planar support surface.
In pending application Serial No. 365,520, a common air flow source is provided for both raising the vehicle, creating the frictionless air film, and for propelling the vehicle. In that respect, the vehicle comprises an upper deck means defining the top of the plenum chamber in the vehicle with a flexible perforated film sheet or membrane extending beneath the upper deck means. The upper deck means is shaped and configured to define a permanently open plenum and closed by the deck means and the underlying flexible film sheet. In a preferred form, a propellor constitutes the propulsion means which moves the air and creates air for pressurization of the plenum chamber. Part of the air flow is directed through a plenum inlet in the deck and part of the flow is directed off to the side of the vehicle (to the rear) to propel the vehicle which is preferably narrowed along its sides towards the bow in a forward direction across the surface of the land or water upon which it resides.
While such air pallet material and personnel handling and transport devices operate satisfactorily, they have certain drawbacks. In the material handling areas where the air pallet functions to replace conventional wooden pallets, irrespective of the creation of a thin air film between the flexible sheet and the underlying support surface, portions of such flexible sheet material often contact rigid elements particularly where the support surface is roughened or has objects projecting upwardly therefrom. Where holes or slots permeate the support surface, the flexible film tends to project into the slots or holes. In the area of pending application Ser. No. 365,520, where the air pallet constitutes a motorized self-propelled vehicle, such vehicles tend to move rapidly and fairly well over the surface of a body of water. However, where the vehicle is contemplated as being movable, not only on water, but on land, once the vehicle leaves the water, it encounters on the land relatively rough surfaces, and the flexible film has been found to be too fragile for extended use, particularly over rough terrain.
Additionally, irrespective of the nature of the use of the air pallet, when subjected to fairly heavy loads, the extent of jacking provided by the flexible film is limited by the load itself and the ability to move over and about obstructions encountered during travel over the supporting surface becomes limited, while at the same time the air film is destroyed during direct frictional contact occurring between the obstruction and the flexible film sheet, with resulting abrasion and even puncture of the sheet as a result of such encounter.
It is, therefore, a primary object of the present invention to provide an improved air pallet for moving of a load relative to an underlying generally planar fixed support surface wherein a support surface contact member is interposed between the means forming the air film for the air pallet to prevent wear and/or destruction of the air film generating means, to facilitate support of heavy loads by the air pallet, and to permit the air pallet to traverse rough, irregular terrain.
It is a further object of the present invention to provide an improved material and personnel handling air pallet which has application to air cushioned pallets and vehicles which utilize other than a thin perforated flexible film and in which the pallet is automatically frictionally braked upon removal of the air pressure from the plenum chamber without grounding out the perforated flexible film or its equivalent on the underlying support surface and which facilitates the conforming of the bottom of the air pallet to the configuration to obstacles confronted by the moving pallet and to permit it to easily ride over and conform to the shape of such obstacles.